1. Field of the Invention
The present invention relates to a flow control apparatus for construction heavy equipment, in which a flow control valve and a directional control valve is provided in a block of the main control valve, thereby performing flow control function of keeping a set flow rate constant regardless of load pressure of an working unit and pump pressure of a hydraulic pump as well as function of a directional control valve.
More particularly, the present invention relates to a flow control apparatus capable of securing stability of a hydraulic system by performing function of a check valve for preventing backflow and function of a pressure compensating flow control valve and thus, by avoiding a sharp change in flow rate and pressure supplied to the working unit even when fluctuations in load pressure of a working unit and pump pressure of a hydraulic pump take place.
2. Description of the Related Art
FIG. 1 is a hydraulic circuit diagram of a conventional flow control apparatus for construction heavy equipment.
The conventional flow control apparatus for construction heavy equipment includes a hydraulic pump 200, a hydraulic cylinder 300 which is driven by hydraulic fluid supplied from the hydraulic pump 200, a control valve 100 which is fitted in a fluid channel between the hydraulic pump 200 and the hydraulic cylinder 300 and drives the hydraulic cylinder 300 by controlling the hydraulic fluid, and a flow control valve 400(400A and 400B) which is fitted in a load passages 6A and 6B between the control valve 100 and the hydraulic cylinder 300 and controls driving speed of hydraulic cylinder 300 by restricting flow rate supplied to the hydraulic cylinder 300. Among reference numerals not described, 4 indicates a center bypass passage, 500 indicates a relief valve for draining the hydraulic fluid to a tank T when a load exceeds the set pressure of the hydraulic circuit.
When a operation lever (not shown) is manipulated and thus a pilot signal pressure is applied to a right end of the control valve 100, the hydraulic fluid discharged from the hydraulic pump 200 passes through the load passage 6A via a pump passage 5, a check valve 3 and the control valve 100 switched in position, and then is supplied to a large chamber 302 of the hydraulic cylinder 300. The hydraulic fluid discharged from a small chamber 301 of the hydraulic cylinder 300 is returned to the tank T via another check valve 405B and the load passage 6B, so that the hydraulic cylinder 300 is driven for extension.
On the other hand, the control valve 100 is switched to the right, the hydraulic fluid discharged from the hydraulic pump 200 is supplied to the small chamber 301 of the hydraulic cylinder 300, so that the hydraulic cylinder is contracted.
When it is intended to control the driving speed of the hydraulic cylinder 300 by restricting the flow rate supplied to the hydraulic cylinder 300 according to a working condition, the flow rate introduced into the large chamber 302 is controlled by the difference between the pilot pressure 403A corresponding to an amount in which a throttle 401A is opened and the spring force preset by a valve spring 404A.
However, according to the conventional flow control apparatus, in order to fit the flow control valve 400 in a fluid channel between the load passages 6A and 6B of the control valve 100 and the hydraulic cylinder 300, a separate block is required, so that the number of components is increased, and thus a cost price is increased. Further, the design is limited because of the interference of the installation positions between the components.
In addition, the conventional flow control valve 400 is not provided with a check function capable of coping with the case that load pressure on the side of the hydraulic cylinder 300 is higher than discharge pressure on the side of the hydraulic pump 200, so that the check valve 3 must be separately fitted in a pump passage 5 of the control valve 100.